Thermal neutrons are low energy neutrons that exist naturally in the environment. Thermal neutrons can penetrate materials used in buildings (e.g., concrete, steel, or glass) as well as common computer and integrated circuit related materials (e.g., copper, aluminum, plastics, solder, or mold compounds for electronics packaging). Penetration of thermal neutrons into electronics packaging may cause malfunctions and/or reduce processing speeds in integrated circuits inside the electronics packaging due to capturing of the thermal neutrons.
When a thermal neutron is captured by the nucleus of certain elements located inside the electronics packaging, a nuclear reaction might occur. The nuclear reaction may generate charged particle emission from the nucleus. The emitted charged particles may upset the voltage or amount of stored charges in an integrated circuit or other device located inside the electronics packaging. Such upset in voltage or amount of stored charges may cause malfunction in the integrated circuit.
Current approaches to reducing the effects of thermal neutron penetration include design approaches (e.g., circuit design approaches) such as providing higher charges and/or higher voltages to reduce the effect of thermal neutron generated charged particles, or logic design and architectural techniques such as the use of checksum, error correcting code, or triple modular redundancy. Such approaches, however, use additional area to the integrated circuit, increase power consumption, decrease performance, and create additional design complexity.
Another approach to reduce the effects of thermal neutron penetration includes eliminating the use of elements that have a high thermal neutron absorption cross section (i.e., a high probability that the nucleus of the element will absorb thermal neutrons) in the semiconductor manufacturing process and, thus, in the final integrated circuit/semiconductor device structure. For example, borophosphosilicate glass (BPSG) has been widely used as an interlayer dielectric and planarization material. The element boron is known to have a high thermal neutron absorption cross section. Thus, moving away from the use of BPSG towards other interlayer dielectric materials may reduce potential detrimental effects due to thermal neutron absorption.
Yet another approach is to use the 11boron isotope and eliminate the use of the 10boron isotope since a 11 boron nucleus can absorb a thermal neutron and remain stable (not emit any charged particles) while the 10boron nucleus generates charged particles (e.g., a Li-7, an alpha particle, and a gamma ray photon) when absorbing a thermal neutron. However, even with the removal of BPSG and/or the switch to the 11boron isotope, many integrated circuits may still exhibit a significant level of sensitivity to thermal neutrons. Thus, since most current electronics and integrated circuit packaging materials have ineffective barriers against thermal neutron penetration, there is a need for materials and/or techniques to mitigate the penetration of thermal neutrons and the effects of thermal neutron penetration.